The invention relates generally to serial production of workpieces by injection moulding and to their treatment subsequent to the injection-moulding step of the production process. The invention relates specifically to the combination of the workpieces and the arrangement made for their transport so as to allow versatile handling of the workpieces.
Finnish Patent Application No 963873 discloses a production process and apparatus, in which semi-finished workpieces are connected in succession and possibly also in parallel by connecting bridges. FIG. 1 shows how the workpieces produced in a given production step from an elongated continuous band, which is wound up in a roll 4. Regarding the example of the figure, it is conceivable that the raw material used is injection-moulded plastic and the products 1 to be prepared are small plastic objects. For the successive objects not to be detached, the jaws of the clamp in FIG. 3 have been shaped so that the xe2x80x9crear endxe2x80x9d (right-hand end in the figure) of each workpiece will comprise a small plastic tongue, which is superfluous in terms of the shape intended for the product. When the following workpiece is injection moulded, a small plastic tongue will also be formed at its xe2x80x9cfront endxe2x80x9d (left-hand end in the figure), the tongue being superfluous in terms of the shape intended for the product and being fastened by melting to the tongue at the rear end of the preceding workpiece. A bridge 2 made of the same material as the actual work-pieces will be formed between the successive workpieces.
FIG. 2 illustrates the surface treatment included in the same production process. The band formed of workpieces is brought to the surface treatment wound up as a roll 6. The workpieces are guided as a band to a dip varnishing basin 7, and from there on to surface paint spraying 8 and to a drying machine 9. Other surface treatment steps given by way of example and illustrated in FIG. 3 are printing 10, gluing 11 of a sticker or a label, and laser production 12 of an identifying pattern. Two optional operations are presented as the last step in the figure. In the first option, the laser cutter 13 separates the workpieces 15 from the band, and after this they have to be handled as individual pieces in general. In the second option, the finished workpieces are further wound up as a roll 14 or bent into a pile, allowing them to be readily transported and placed in the assembly step of a more complex product.
Nonetheless, the prior art method described above has proved awkward in the practice, because the bridges made of injection-moulded material and connecting the successive workpieces do not withstand all process steps properly. In addition, they limit the handling of the band of workpieces in some process steps.
The typical feature of production methods based on solidification of a liquid or a viscous production material is that the material is guided to the desired locations of the mould through one or more xe2x80x9cpouring channelsxe2x80x9d. In the solidification step, there is still material in the pouring channels, and thus this portion of the material will form a sprue. The actual workpiece and the sprue are connected by a thin material bridge at the point where the pouring channel has been connected to the mould of the workpiece proper. The sprue is often utilised in tie further processing of the workpiece, because e.g. surface treatment intended to cover the entire workpiece surface is easy to carry out by holding the sprue. U.S. Pat. No. 5,478,051 discloses a method in which the plastic parts to be injection moulded, after having been pressed, form a band, in which a separate reinforcing wire passes through the sprues and connects successive parts. The publication describes both embodiments in which the wire consists of the same material as the injection-moulded pieces and embodiments in which the wire is e.g. a metal wire. Similar solutions are disclosed in patent specifications U.S. Pat. Nos. 4,008,302 and 3,192,298.
However, the solutions above are disadvantageous in terms of their manufacturing techniques, because they cannot be subjected to, say, dip varnishing, without the band assisting also in the transport or any other auxiliary equipment being immersed in varnish. Thus, the auxiliary equipment will usually be fit for use only once, because recycling of the equipment would result in detrimental varnish accumulation in the apparatus.
The object of the present invention is a method and an apparatus for producing injection-moulded workpieces so as to allow versatile further processing of the workpieces without a disposable transport arrangement. Another object of the invention is to allow the workpieces to be exactly aligned in the different steps of the production process.
The objects of the invention are achieved by providing the workpieces with fasteners enabling them to be connected to the transport arrangement so that the fastening can be partly released, and then the partly released fasting allows the workpiece to be shifted in at least two different positions relative to the transport arrangement.
The method of the invention comprises steps for
a) forming the workpiece by injection moulding so that the workpiece is fastened to a given elongated transport arrangement during the injection moulding
b) moving the workpiece forwards in the production process by means of the elongated transport arrangement.
The method is characterised by comprising steps for
c) partly releasing the fastening of the workpiece from the elongated transport arrangement
d) shifting the workpiece supported by the remaining fastening between itself and the transport arrangement into a position where it is substantially outside the plane defined by the transport arrangement
The invention also relates to an apparatus comprising
a mould for producing workpieces by injection moulding
an elongated transport arrangement for moving the injection-moulded workpieces forward in the production process;
the apparatus having a mould disposed to form fastening members in the workpieces for fastening the workpieces to the transport arrangement.
The method is characterised by comprising
means for partly releasing the fastening of the workpieces from the transport arrangement
means for shifting a workpiece whose fastening to the transport arrangement has been partly released into a position relative to the transport arrangement, where it is located substantially outside a plane defined by the transport arrangement
In accordance with the invention, fastening members are formed in the workpieces during the injection moulding to connect the workpieces with the transport arrangement, which is intended to transfer the workpieces between the different steps of the production process. At least part of the fastening members are made removable. Removable fastening members can also be formed so that they can be refastened after having been unfastened. When all the fastening members are fastened, the workpieces have a specific first position relative to the transport arrangement. In this position they are easy to align accurately in a given step of the production process, because the fastening members, any separate aligning members connected with these, and the parts of the transport arrangement to which the fastening members are fastened, can be used as mechanical aligning means.
When part of the fastening members have been unfastened, the workpiece can be turned into a second position while being supported by the remaining fastening members. The workpiece can be conceived as substantially planar, and then the direction of its plane in the first position is substantially the same as the direction of a given plane defined by the transport arrangement. In the second position, the workpiece can be turned so that the direction of its plane deviates notably from the direction of the plane defined by the transport arrangement. If the fastened fastening members are at a given edge of the workpiece, the workpiece will in its second position, be principally located quite far from the plane defined by the transport arrangement, and can then be e.g. immersed in a vessel containing a surface treatment agent without the transport arrangement getting into contact with this surface treatment agent.
The transport arrangement considered most advantageous comprises one or more band-like or chain-like conveyors forming a closed loop. The conveyor is called a chain for the sake of conciseness. At regular intervals the one or more chains are provided with attachment points, and at each of these a given axis can be fastened. The transport arrangement and the injection-moulding mould are mutually positioned such that when the mould is closed, at least one was will remain within it. Thus fastening members are formed on the injection-moulded workpiece to attach this to at least one axis. It is preferable to fasten the injection-moulded workpiece to two successive axes, and then at least the fastening members attached to one of the axes will be removable. When the fastening is released from one axis, the workpiece will remain supported by the other axis, and can then be rotated about this axis into the desired position.